Thermostatic snap acting switch



Jan. 6, 1959 N; MILLER THERMOSTATIC SNAP ACTING SWITCH Filed May 21.1957 Ma ma Mil/e2" THERMOSTATIC SNAP ACTENG SWITCH Nicholas Miller,Chicago, Ill., assignor to The Dole Vaive Company, Morton Grove, Ill., acorporation of Illinois Application May 21, 1957, Serial No. 669,633

11 Claims. (Cl. 200-444 This invention relates to improvements inthermostatic control devices and more particularly relates to athermostatically operated snap acting switch adapted for controlling theoperation of air conditioners and the like. I

A principal object of the invention is to provide a simple form ofthermostatically operated switch in which the temperature of operationof the switch may be adjusted at the selection of the operator.

A further object of the invention is to provide a simple and improvedthermostatic snap acting switch arranged with a view toward utmosteificiency and compactness.

Still another object of the invention is to provide a thermostaticallyoperated snap acting switch for air conditioners and the like in whichthe temperature range of operation of the switch may be adjusted at theselection of the operator, and having a snap lever operating the snapblade for the switch and acted on by the thermal element of the switch,in which the points of application of the forces acting on the snaplever lie substantially in the same plane and in the mid-position of thetemperature adjustment of the switch the direction of the forces issubstantially perpendicular to said plane, thereby reducing friction andincreasing the efiiciency of operation of the switch.

Still another object of the invention is to provide a thermostaticallycontrolled snap acting switch particularly adapted for air conditionersand the like in which a thermal element having an extensible powermember acting against a lever is provided to operate the snap blade forthe switch, and in which the fulcrum for the lever is yieldable toaccommodate over-travel of the power member of the thermal elementwithout injury to the switch.

A still further object of the invention is to provide a simple andimproved form of thermostatically controlled snap acting switch in whicha power type of thermal element having an extensible power member servesto operate and acts against one end of a snap lever for operating theswitch, in which the fulcrum for the snap lever is adjustable to varythe temperature range of operation of the switch, and in which anover-travel safety spring biases the fulcrum for the snap lever in itsextended position, and is incorporated within the adjusting means forthe snap lever and yields upon overtravel conditions, to accommodateover-travel of the power member of the thermal element without injury tothe snap acting switch.

These and other objects of the invention will appear from time to timeas the following specification proceeds and with reference to theaccompanying drawing wherein:

Fig. 1 is a transverse sectional view taken through a thermostatic snapacting switch constructed in accordance with the invention;

Fig. 2 is a view in side elevation of the switch shown in Fig. l, withan end cover for the switch casing removed and certain other partsremoved and shown in section; and

Fig. 3 is a fragmentary detail sectional view illustrating MeijiPatented Jan. 6, 1959 the relative positions of the reaction points ofthe switch actuating mechanism with respect to each other.

In the embodiment of the invention illustrated in the drawing, a frame10 generally U-shaped in cross-section and having parallel legs 11 and12 extending from the base of the U forms the frame for the casing forthe switch. The leg 11 has a casing 13 of a thermal element 15 extendingtherethrough, with a clamping ring 16, clamping the casing 13 of thethermal element to a cylinder 17 thereof, maintained in abuttingengagement with the inner side of the leg 11 by a return spring 19 ofthe thermal elementlS.

The leg 12 is shown as having an anchor 20 for a dial knob (not shown)abutting the outer side thereof and rotatably mounted on an internallythreaded boss 21 extending through the leg 12. and spun or otherwisesecured thereto. A friction spring washer 22 is shown as beinginterposed between a shoulder 23 of the boss 21 and the inner face ofthe portion of the anchor 20 engaging the outside of the leg 12, toprevent unintentional rotation of said anchor.

The boss 21 is shown as having a hollow adjusting screw 24 threadedtherein and extending within the inside of the leg 12 into the interiorof the switch casing. The hollow adjusting screw 24 forms an adjustablemounting for a plunger 25 slidably extending therethro-ugh and forming afulcrum for a snap or actuating lever 27 at its inner end. The term snaplever is not intended to designate the lever 27 as a lever that moveswith a snap action, but is used to refer to the lever as the actuatingmeans for the snap acting switch, as will more clearly appear as thespecification proceeds. A relatively heavy over-travel safety spring 29is mounted within the hollow adjusting screw 24 and abuts a head 30 ofthe plunger 25 at its inner end and a disc 31 at its outer end, shown asbeing retained within the hollow adjusting screw 24 by staking an innerwall portion of the adjusting screw into engagement therewith.

The over-travel safety spring 29 is sutliciently strong to normally actas a solid member and hold the plunger 25 in position to provide a fixedfulcrum for the snap lever 27, but to accomodate the plunger 25 to yieldupon over-travel of a power member of piston 33 of the thermal element,to prevent damage to a snap blade 35 of a snap acting switch 36, uponover-temperature conditions and upon conditions where the plunger 25 isadjusted to eliect operation of the switch at a substantially lowertemperature than the ambient temperature to which the thermal element issubjected.

A calibration plate 37 is fixed to the adjusting screw 24 and has an arm39 engageable with the anchor 20, to effect turning movement of thecalibration plate 37 and the adjusting screw 24 upon turning movement ofthe anchor 20, as by a dial knob (not shown), to vary the spacingbetween the inner end of the plunger 25 and a reduced diameter engagingend 40 of the power member 33 of the thermal element 15. The fartheraway the inner end of the plunger 25 is from the end of the reduceddiameter end 40 of the power member 33, the greater will be the travelof said power member required to pivot the snap lever 27 and effectclosing of the switch 36. Adjustable movement of the end of the plunger25 away from the reduced diameter end of the power member 33 will,therefore, increase the temperature at which the switch 36 closes. In acontrary manner, adjustable movement of the end of the plunger 25 towardthe reduced diameter end 40 of the power member 33 will reduce thetravel of the power member 33 required to effect closing of the switch36,,and will therefore reduce the temperature at which said switchoperates.

At temperature conditions where the ambient temperature is and theswitch is set to close at 90, and it is .7 a desired that the switchclose at 70, turning of the adjusting screw 24 to position the plunger25 to effect closing of the switch at 70 will effect compression of thespring 29, the spring returning as the piston 40 is retracted bylowering of the ambient temperature to 70.

The thermal element 15 is shown as being a well known form of power orhigh motion type of thermal element in which a fusible thermallyexpansible material con tained within the casing 13 acts against adiaphragm (not shown) clamped within said casing by the clamping ring16, to extend the power member 33 with respect to the cylinder 17 onincreases in temperature sufficient to effect fusion of the fusiblethermally expansible material contained within the casing 13, as shownand described in Patent No. 2,368,181 which issued to Sergius Vernet onJan. 30, 1945, and no part of the present invention, so not herein shownor described further.

The power member 33 is returned within the cylinder 17 upon reductionsin temperature by the spring 19 seated at one end in a spring seat 41having a right angled portion 43 riveted or otherwise secured to thebase of the U-shaped frame 10, with the spring seat 41 extendinginwardly from said base within the switch casing. The opposite end ofthe return spring 19 is seated on a flange 44 of a generally cylindricalspring saddle or retainer 45, encircling the cylinder 17 and mounted asits outer end on the reduced diameter end 40 of the power member 33 andabutting the shoulder formed at the junction of said reduced diameterend with the enlarged diameter portion of the power member 33.

The snap acting switch 36 is shown as comprising a spring metal switcharm 47 riveted or otherwise secured to an inturned leg 49 of a terminal50, extending through an end cover 51 for the switch casing, andinsulated therefrom. The switch arm 47 is preferably made from a springmaterial having good electrical conductivity, such as commercial bronzeor beryllium copper and has a contact 53 on its free end, engageablewith a stationary contact 54 on an inturned leg 55 of a terminal 56,extending through and suitably insulated from the end cover plate 51.The resilient switch arm 47 is biased to normally maintain the movablecontact 53 in engagement with the stationary contact 54.

The contact 53 is moved to an open position with respect to the contact54 by operation of the snap blade 35 through an operator 57, which maybe in the form of an insulator rod having a reduced diameter end 59extending through the switch arm 47 and having a second reduced diameterend 60 extending through the snap blade 35, so that snapping of theblade 35 into the position shown in Fig. 1 into engagement with a stop63, will effect opening of the contact 53 with respect to the contact54.

The snap blade 35 may be made from stainless steel and is mounted at itsend opposite the stop 63 on a leg 66 of a snap blade support 67. Thesnap blade support 67 has lateral projections 69 projecting laterallyfrom opposite sides thereof and engaging within generally V-shapedfulcrum notches 70, formed in opposite parallel spaced legs 71 of abracket 72, mounted on the inner side of the leg 12 of the switchcasing.

The snap blade support 67 also has an arm 73 extending outwardlytherefrom at generally right angles with respect to the snap blade 35,and having nibs 74 extending laterally from opposite sides thereof andengaging within bearing slots 75 formed within parallel spaced legportions 76 of the snap lever 27, adjacent the end of said snap leveropposite from the power member 33 of the thermal element 15.

The inner end of the plunger 25 engages the snap lever 27 intermediatethe ends thereof within a recess 77,

formed in a base 79 of said snap lever and recessed adistance sufficientto position the point of engagement of the plunger 25 with the snaplever in a plane extending through the point of engagement of thereduced diam eter end 40 of the power member 33 with the base 79 of thesnap lever and the point of engagement of the bearing slots with thenibs 74 of the snap blade support 67 and the center of rotation ofprojections 69 in notches 7! Thus, the points of application of theforces acting on the snap lever 27 lie substantially in the same plane,and in the mid-position of the temperature adjustment of the switch, thedirection of the forces is substantially perpendicular to said plane.

The free end of the snap blade 35 engages within a recessed portion 80of an overcenter spring 81. The overcenter spring 81 is shown as beinggenerally U-shaped in cross-section, and as having a tongue 83projecting from its opposite leg from the recess 80, and having rockingengagement within a recessed portion 84 of the leg 11 of the switchcasing.

The overcenter spring 81 besides serving as an overcenter spring to holdthe snap blade 35 into engagement with the stop 63 to hold the contactsof the switch 36 in an open position, and also to hold the snap blade 35into engagement with a stop 85 to accommodate closing of the contacts 53and 54- by the bias of the spring arm 47, exerts a substantiallyconstant force on the end of the snap blade 35, to cause said snap bladeto snap the contact 53 into an open position, and to accommodate thecontact 53 to engage the contact 54 with a snap action.

A return spring blade 87 is provided to return the snap blade support 67and snap lever 27 upon cooling of the thermal element and retractiblemovement of the power member 33 with respect to the cylinder 17 of thethermal element. The return spring blade 87 is shown as extending alongthe snap blade support 67 and snap blade 35 and as being riveted to saidsnap blade support by the rivets securing the snap blade 35 to saidblade support. The return spring 57 is biased outwardly from the snapblade support 67 and snap blade 35 toward the thermal element 15 and hasengagement at its inner end with an abutment 38 extending within theswitch casing, from the base of the U-shaped frame 10 of said swltchcasing, and biases the snap blade 35 and snap blade support 67, as wellas the snap lever 27, in a direction to effect opening of the contacts53 and 54, as the power member 33 retractibly moves within the cylinder17 of the thermal element 15.

A stop 89 extending inwardly from the base of the U-shaped casingportion 10, is provided to l1m1t pivotal movement of a snap lever 27 ina counterclockwise direction upon over-temperature conditions andover-extension of the power member 33 of the thermal element, as theplunger 25 retractibly moves against the over-travel safety spring 29.

In operation of the switch, as the temperature to which the casing 13 ofthe thermal'element 15 is sub ected rises to an extent suflicient toeffect fusion of the fusible thermally expansible material containedwithin the easing 13, the power member 33 will extensibly move wlthrespect to the cylinder 17 and fulcrum the snap lever 27 about the innerend of the plunger 25. Thls in turn will pivot the snap blade supportabout the bearing recesses 70 in the bearing brackets 71 against thereturn spring 87. As the snap blade support 67 pivots a distancesufficient to bring the free end of the snap blade 35 past dead centerwith respect to theovercenter snap spring 81, the overcenter spring 81will exert a force on the end of the snap blade 35 and cause said snaplever to snap into engagement with the stop 85 and accommodate thecontact 53 to snap into engagement with the contact 54, by the bias ofthe resilient blade 47. As the temperature to which the casing 13 of thethermal element 15 is subjected is reduced to an extent sufficient toaccommodate the spring 19 to retractibly move the power member 33 withrespect to the cylinder 17, the return spring 87 will pivot the snapblade support 67 and snap lever 27 in a clockwise direction until theend of the snap blade 35 has passed a dead center position with respectto the overcenter spring 81, at which time said overcenter spring willsnap the snap blade intoen-' gagement with the stop 63 and open thecircuit between the contacts 53 and 54 with a snap action.

It will be understood that various modifications and variations of thepresent invention may be effected without departing from the spirit andscope of the novel concepts thereof.

I claim as my invention:

1. A thermostatic snap acting switch comprising a switch casing, arockable snap blade and lever within said casing and respectivelypivotable about parallel axes, an overcenter spring rockingly mounted atone end in said casing in advance of said snap blade and having rockingengagement with said snap blade at its opposite end, means operatingsaid snap lever to move said snap blade in a direction to effect closingof an energizing circuit comprising a thermal element having a powermember extensibly movable upon increases in temperature and havingoperative engagement with said snap lever, and a fulcrum for said snaplever disposed within said casing on the opposite side of said leverfrom said power member and selectively adjustable from the outside ofsaid casing to vary'the temperature range of operation of said switch.

2. A thermostatic snap acting switch comprising a switch casing, arockable snap blade and lever within said casing and respectivelypivotable about parallel axes, an overcenter snap spring rockinglymounted at one end in said casing in advance of the end of said snapblade and having rocking engagement with said blade at its opposite end,a switch operated by said snap blade, means operating said snap levercomprising a thermal element having an extensible power memberengageable with an end of said snap lever, a fulcrum for said snap leverengageable with said snap lever intermediate the ends thereof on theopposite side of said lever from said power member, and yieldable meansbiasing said fulcrum into an extended fulcrum position within saidcasing and yieldable to accommodate over-travel of said power memberupon over-temperature conditions.

3. A thermostatic snap acting switch comprising a switch casing, arockable snap blade and snap lever within said casing, an overcentersnap spring rockingly mounted in said casing in advance of said snapblade and having rocking engagement with said snap blade, a switchoperated by said snap blade, means operating said snap lever in onedirection to effect snap operation of said switch into one position,comprising a thermal element mounted in said casing having an extensiblepower member engageable with said snap lever, a fulcrum for said snaplever extending within said casing and adjustable from the outside ofsaid casing to vary the position of said fulcrum with respect to saidpower member and thereby vary the temperature range of operation of saidswitch, and yieldable means contained within the adjusting means forsaid fulcrum, biasing said fulcrum into an extended fulcruming positionand yielding upon over-travel of said power member to prevent damage tosaid snap blade upon over-temperature conditions.

4. In a thermostatic snap acting switch, a switch casing, a snap bladewithin said casing, a support for one end of said snap blade rockinglymounted within said casing and respectively pivotable about parallelaxes, a snap lever having operative connection with said support inspaced relation with respect to said snap blade for rockably moving saidsupport and snap blade, an overcenter snap spring rockingly mounted insaid casing in advance of said snap blade and having rocking engagementwith the free end of said snap blade, a thermal element having anextensible power member engageable with said snap lever, a fulcrum forsaid snap lever extending parallel with said power member and havingengagement with said snap lever intermediate the ends thereof on theopposite side of said lever from said power member, and means operablefrom the outside of said switch casing for moving said fulcrum toward orfrom said power member and thereby varying the temperature range ofoperation of said snap blade.

5. In a thermostatic snap acting switch, a casing, a snap blade withinsaid casing, a support therefor rockingly mounted within said casing, asnap lever connected at one of its ends with said support in parallelspaced relation with respect to the axis of rocking movement thereof,for rockably moving said support and snap blade,

an overcenter snap spring rockingly mounted in said casing in advanceofsaid snap blade and having rocking engagement with said snap blade, athermal element mounted in said casing and having an extensible powermember extending generally parallel to said snap blade and extensibleupon predetermined increases in temperature, an engaging connectionbetween said power mem her and said snap lever at the end thereofopposite said support, a fulcrum for said snap lever extending generallyparallel to said power member and having engagement with said snap leverintermediate the ends thereof on the opposite side of said lever fromsaid power member, means selectively operable from the outside of saidcasing for moving said fulcrum toward or from said power member to varythe temperature range of operation of said snap blade, and a springbiasing said fulcrum in extended relation with respect to said casingand normally acting as a solid member and yielding upon over-travel ofsaid power member upon over-temperature conditions.

6. In a thermostatic snap acting switch particularly adapted for airconditioners and the like, a casing, a snap blade within said casing, asupport therefor rockingly mounted within said casing, a snap leverconnected at one end with said support in spaced relation with respectto the axis of rocking movement thereof for rockably moving said supportand snap blade, a yieldable switch arm spaced from said snap blade andhaving a contact thereon biased by said switch arm into one position, anoperator connecting said snap blade with said switch arm for operatingsaid switch arm to move said contact into another position, anovercenter snap spring rockingly mounted in said casing in advance ofsaid snap blade and having rocking engagement with the end of said snapblade, a thermal element having an extensible power member extendinggenerally parallel to said snap blade, an engaging connection betweensaid power member and the opposite end of said snap lever from saidsupport, a fulcrum extending within said casing generally parallel tosaid power member and having engagement with said snap leverintermediate its ends, and means operable from the outside of saidcasing for adjusting the position of said fulcrum with respect to saidpower member and the temperature range of operation of said switch arm,said means including an over-travel spring biasing said fulcrum into afulcruming position and normally acting as a solid member andaccommodating retractible movement of said fulcrum upon over-travel ofsaid power member effected by over-temperature conditions.

7. In a thermostatic snap acting switch, a switch casing, a snap bladewithin said casing, a support for said snap blade, means mounting saidsupport for rocking movement comprising a fixed fulcrum, an armextending from said support generally perpendicular to said snap blade,a snap lever having rocking engagement with said arm at one end inoutwardly spaced relation with respect to said fixed fulcrum, a fulcrumfor said snap lever disposed within said casing and having engagementwith said snap lever intermediate the ends thereof, a thermal elementmounted in said casing and having a power member extending generallyparallel to said fulcrum for said snap lever and extensible uponpredetermined increases in temperature and engaging the opposite side ofsaid lever from said fulcrum for said lever, an overcenter snap springrockingly mounted in said casing in advance of said snap blade andhaving rocking engagement with the free end of said snap blade, and areturn spring secured to said snap blade and support and biasing saidsnap blade and support to cause said snap lever to follow said powermember upon retractible movement thereof, upon reductions intemperature, the center of rotation of said snap blade support relativeto said fixed fulcrum and the points of engagement of said snap leverwith said arm on said snap blade support and of said fulcrum with saidsnap lever and of said power member with said snap lever all beingsubstantially in a single plane and the direction of all forces actingon said snap lever being substantially perpendicular to said plane,thereby reducing sliding friction upon operation of said lever.

8. In a thermostatic snap acting switch, a switch casing, a snap bladewithin said casing, a support for said snap blade, means mounting saidsupport for rocking movement comprising a fixed fulcrum, an armextending from said support generally perpendicular to said snap blade,a snap lever having rocking engagement with said arm at one end inoutwardly spaced relation with respect to said fixed fulcrum, a fulcrumfor said snap lever disposed within said casing and having engagementwith said snap lever intermediate the ends thereof, a thermal elementmounted in said casing and having a power member extending generallyparallel to said fulcrum for said snap lever and extensible uponpredetermined increases in temperature and engaging the opposite side ofsaid lever from said fulcrum for said lever, an overcenter snap springrockingly mounted in said casing in advance of said snap blade andhaving rocking engagement with the free end of said snap blade, and areturn spring secured to said snap blade and support and biasing saidsnap blade and support to cause said snap lever to follow said powermember upon retractible movement thereof, upon reductions intemperature, the center of rotation of said snap blade support relativeto said fixed fulcrum and the points of engagement of said snap leverwith said arm on said snap blade support and of said fulcrum with saidsnap lever and of said power member with said snap lever all beingsubstantially in a single plane and the direction of all forces actingon said snap lever being substantially perpendicular to said plane whenthe temperature adjustment for said switch is in mid-position, therebyreducing sliding friction upon operation of said lever, said fulcrum forsaid snap lever comprising a plunger and a hollow screw threaded withinsaid casing and carrying said plunger and adjustably movable to vary theposition of the end of said plunger with respect to said power memberand the temperature range of operation of said switch.

9. In a thermostatic snap acting switch, a switch casing, a snap bladewithin said casing, a support for said snap blade, means mounting saidsupport for rocking movernent comprising a fixed fulcrum, an armextending from said support generally perpendicular to said snap blade,a snap lever having rocking engagement with said arm at one end inoutwardly spaced relation with respect to said fixed fulcrum, a fulcrumfor said snap lever disposed within said casing and having engagementwith said snap lever intermediate the ends thereof, a thermal elementmounted in said casing and having a power member extending generallyparallel to said fulcrum for said snap lever and extensible uponpredetermined increases in temperature and engaging the opposite side ofsaid lever from said fulcrum for said lever, an overcenter snap springrockingly mounted in said casing in advance of said snap blade andhaving rocking engagement with the free end of said snap blade, a returnspring secured to said snap blade and support and biasing said snapblade and support to cause said snap lever to follow said power memberupon retractible movement thereof, upon reductions in temperature, saidfulcrum for said snap lever comprising a plunger and a hollow screwthreaded within said casing and carrying said plunger and adjustablymovable to vary the position of the end of said plunger with respect tosaid power member and the temperature range of operation of said switch,and an over-travel spring contained within said hollow screw and biasingsaid plunger in extended relation with respect to said screw andaccommodating retractible movement of said plunger upon over-travel ofsaid power member, the center of rotation of said snap blade supportrelative to said fixed fulcrum and the points of engagement of said snaplever with said arm on said snap blade support and of said plunger withsaid snap lever and of said power member with said snap lever all beingsubstantially in a single plane and the direction of all forces actingon said snap lever being substantially perpendicular to said plane whenthe temperature adjustment for said switch is in mid-position, therebyreducing sliding friction upon operation of said lever.

10. In a thermostatic snap acting switch particularly adapted for airconditioners and the like, a casing, a snap blade within said casing, asupport therefor rockingly mounted withinsaid casing, a snap leverconnected at one end with said support in spaced relation with respectto the axis of rocking movement thereof for rockingly moving saidsupport and snap blade, a fulcrum within said casing having engagementwith said snap lever intermediate its ends, thermostatic means engagingthe opposite end of said snap lever from said support for actuating saidlever, an overcenter snap spring rockingly mounted in said casing inadvance of said snap blade and having rocking engagement with the end ofsaid snap blade, a yieldable switch arm spaced from said snap blade andhaving a contact thereon biased by said switch arm into one position,said snap blade and switch arm extending in general parallel relationwith respect to each other, and an operator connecting said snap bladewith said switch arm for operating said switch arm to move said contactinto another position.

11. In a thermostatic snap acting switch particularly adapted for airconditioners and the like, a casing, a snap blade within said casing, asupport therefor rockingly mounted within said casing, a snap leverconnected at one end with said support in spaced relation with respectto the axis of rocking movement thereof for rockably moving said supportand snap blade, a yieldable switch arm spaced from said snap blade andhaving a contact thereon biased by said switch arm into one position, anoperator connecting said snap blade with said switch arm for operatingsaid switch arm to move said contact into another position, anovercenter snap spring rockingly mounted in said casing in advance ofsaid snap blade and having rocking engagement with the end of said snapblade, a

thermal element having an extensible power member extending generallyparallel to said snap blade, an engaging connection between said powermember and the opposite end of said snap lever from said support, afulcrum extending within said casing generally parallel to said powermember and having engagement with said snap lever intermediate its ends,and means operable from the outside of said casing for adjusting theposition of said-fulcrum with respect to said power member and thetemperature range of operation of said switch arm.

References Cited in the file of this patent UNITED STATES PATENTS2,611,845 Miller Sept. 23, 1952 2,658,121 Gray et al Nov. 3, 19532,691,084 Miller Oct. 5, 1954 2,738,397 Slonneger Mar. 13, 1956

